Hydrosilylation process

ABSTRACT

A silane or siloxane containing at least one organic group is prepared by a hydrosilylation reaction between a silane or siloxane (A) containing at least one Si—H group and an allyl compound (B) in the presence of a noble metal catalyst. The silane or siloxane (A) and the allyl compound (B) are fed continuously through a reaction zone which is maintained at a temperature in the range 115-200° C. and which is provided with heat exchanger means to dissipate the heat from the exothermic hydrosilylation reaction. The residence time of (A) and (B) in the reaction zone is less than 20 minutes.

[0001] This invention relates to a process for the preparation of asilane or siloxane containing at least one organic group by ahydrosilylation reaction between a silane or siloxane (A) containing atleast one Si—H group and an allyl compound (B). Such processes are knownfor the preparation of various organo-functional siloxanes. Thehydrosilylation reaction is generally carried out as a batch reaction at40-110° C. in the presence of a noble metal catalyst. Examples of suchprocesses are described in U.S. Pat. No. 4,533,744, U.S. Pat. No.4,292,434 and U.S. Pat. No. 5,153,293.

[0002] Pt-catalysed hydrosilylation of materials containing allylicCH2═CH—CH2—unsaturation is generally accompanied by unwantedisomerisation of the allylic double bond to its internal isomerCH3—CH═CH— which is unreactive towards hydrosilylation. This leads to anaccumulation of isomerised, unreacted material in the process which isinefficient in materials usage and may cause problems with productperformance. Furthermore, the presence of the unwanted isomer in someproducts, for example in the hydrosilylation products ofallyl-terminated poly(alkyleneoxide) has been shown to lead to thegeneration of unpleasant odours on ageing. Levels of isomerisation aretypically in the region of 10-30%.

[0003] U.S. Pat. No. 6,191,297 describes the preparation of3-functionalized propylsilanes by the addition of allyl compounds,particularly allyl chloride, to silanes at 0-200 degrees C. and 800 mbarto 6 bar in the presence of a platinum catalyst that has ligandscontaining sulphur. U.S. Pat. No. 6,191,297 teaches that 25-30 mol. % ofthe allyl chloride reacting is normally converted to propene and that ifthe reaction is carried out under pressure, the propene is converted topropylsilanes, which can increase the consumption of trichlorosilane by28%, whereas a process carried out at reduced pressure is more selectiveand gives better yields.

[0004] Other prior proposals to circumvent the unwanted isomerisationhave revolved around replacing the allylic unsaturation by a double bondincapable of undergoing isomerisation (but most of available rawmaterials are allyl-functional) or using expensive separation processes,for example liquid chromatography and/or distillation, to removeunreacted isomerised materials from the product.

[0005] U.S. Pat. No. 6,291,622-B describes a continuous process forhydrosilylation of substances containing C═C bonds by introducing thereactants into a loop-like, heatable and coolable reaction circuit whichhas a static or dynamic mixing element, leaving the reaction mixture inthe reaction circuit (typically for 2 hours) until a predetermineddegree of conversion has been reached and subsequently transferring thereaction mixture to a tube reactor to complete the reaction.

[0006] EP-1146064-A describes effecting a hydrosilylation reactionbetween a liquid organosilicon compound having a Si-bonded H atom and aliquid organosilicon compound having an aliphatic unsaturated bond inthe presence of a platinum catalyst continuously in a tubular reactorequipped with a stirring and plug-flow maintaining apparatus within thereactor.

[0007] A process according to the present invention for the preparationof a silane or siloxane containing at least one organic group by ahydrosilylation reaction between a silane or siloxane (A) containing atleast one Si—H group and a an allyl compound (B) in the presence of anoble metal catalyst, is characterised in that the silane or siloxane(A) and the allyl compound (B) are fed continuously through a reactionzone which is maintained at a temperature in the range 115-250° C. andwhich is provided with heat exchanger means to dissipate the heat fromthe exothermic hydrosilylation reaction, the residence time of (A) and(B) in the reaction zone being less than 20 minutes.

[0008] We have found that when using the process of the presentinvention, the level of unreacted isomerised allyl compound (that is,CH3—CH═CH— compound) in the product stream is generally less than 10mole % and usually less than 5 mole % based on the amount of organicgroups derived from allyl compound (B) incorporated in the siloxane. Formost reactions the level of isomerised compound is less than 1% and inmany reactions the level of isomerised compound is so low, for exampleless than 0.1 mole %, that it is undetectable. We have generally foundincreasing differentiation between the rate of hydrosilylation and therate of isomerisation as we move to higher temperature operation.

[0009] The heat exchanger-reactor does not need internal stirring oragitating devices to effect the reaction, and can achieve 100% (or near)conversions in a single pass.

[0010] The temperature of reaction is preferably at least 120° C. andmost preferably at least 130° C. The maximum temperature depends on thephysical properties and thermal stability of the reactants and products;temperatures in the range 130-200° C. and particularly in the range130-170° C. are preferred. The residence time of the reagents in thereactor is preferably less than 5 minutes, more preferably less than 2minutes and most preferably is less than 30 seconds, for example aresidence time of 1-15 seconds.

[0011] The reactor itself generally needs to be capable of removing theheat generated by the hydrosilylation reaction during the shortresidence time. For this reason the preferred reactor is one withexcellent heat transfer properties, for example a reactor having adesign similar to a heat-exchanger. Several such designs exist includingcommercially available units.

[0012] A preferred type of heat exchanger reactor effectively has areaction zone comprising narrow channels in a block of material of highheat conductivity. The channels generally have a thickness (smallestdimension) of less than 10 mm. and preferably have a thickness less than2 mm., for example they can be tubular of diameter about 1 mm. or may beflat channels of width 1-100 mm., preferably 2-10 mm. and thicknessabout 1 mm. The length of the channels is for example 20 to 800 mm andmay be straight run or multipass within the exchanger. The internalreaction volume of such a heat-exchanger can be as little as 10 mL or asmuch as 1,000 L or even 10,000 L; according to the dimensions of theheat exchanger and manufacturing capabilities. Greater throughputs canalso be obtained by assembling two or more such reactors in parallel,while multi stage reaction systems can be achieved by operating reactorsin series. The use of low volume reactors with a low residence timeallows an adequate production rate while keeping only a low mass ofreagents in the reaction circuit, giving an inherently safer system. Theuse of narrow channels promotes laminar flow with little back-mixing anda good residence time distribution can be attained without the need forthe mixing elements such as those described in EP-1146064 to achieveplug flow, although static or dynamic mixing elements can be present ifdesired to promote mixing of the reagents. The channels can also bedesigned to be continuous or discontinuous as required to aid theresidence time distribution.

[0013] One preferred example is a “pin-fin” heat exchanger, which is atype of plate heat exchanger and consists essentially of a stack of thinmetal plates, adjacent pairs of plates in the stack being separated byspaced columns or “pins”. Fluid flowing through the stack passes betweenadjacent pairs of plates and is forced to follow a tortuous path to flowaround the pins in its travel from one side of the stack to the other.The pins are essentially columns of solid metal which have to be bondedat their ends to a pair of plates so that the pins are sandwichedbetween and perpendicular to the plates. The plates form the primarysurfaces of the heat exchanger and separate different flow streams. Thepins act as the heat exchanger. fins, that is they create the desiredsecondary surfaces. A particularly preferred pin-fin heat exchanger isdescribed in WO-A-99/66280; in this heat exchanger the pins are joinedtogether by ligaments which have a thickness less than that of theplates and extend between adjacent pins.

[0014] Another preferred type of plate heat exchanger reactor isdescribed in WO-A-98/55812. This comprises a bonded stack of perforatedplates. Adjacent plates have their perforations aligned in rows withcontinuous ribs between adjacent rows. Adjacent plates are aligned sothat the rows of perforations in one plate overlap the rows ofperforations in an adjacent plate. The ribs of adjacent plates lie incorrespondence with each other. This construction provides discretefluid channels extending across the plates.

[0015] An alternative preferred type of plate heat exchanger reactor isdescribed in WO-A-00/34728. This reactor has a stacked assembly ofplates each having a first series of slots alternating with a secondseries of slots. When assembled, the first series of slots definepassageways through the stack for a first fluid and the second series ofslots define passageways for a second fluid. The construction is statedto be particularly useful as a packed bed catalytic reactor.

[0016] Other types of heat exchanger can be used as reactor, for examplea scraped surface (also known as a wiped film or thin film) heatexchanger, an enhanced shell and tube heat exchanger or a diffusionbonded heat exchanger. Alternative reactors which can be used in theprocess of the invention are spinning disc reactors, in which thereagents are contacted as a film flowing across a spinning disc.

[0017] The allyl compound (B) is in general any compound containing aCH2═CH—CH2— moiety. In many case, the allyl compound contains afunctional organic group which is introduced by the hydrosilylationreaction into the silane or siloxane. The functional organic group canfor example be a hydroxyl, thiol, epoxide, isocyanate, amine, halide,ether or carboxyl group. A hydroxyl group can for example be an alcoholor ether-alcohol moiety. An amine group can be a primary, secondary ortertiary amine group and may be a polyamine moiety containing forexample secondary and primary amine groups. A halide group can be achlorine, fluorine, bromine or iodine group and includes an organicmoiety having two or more halogen atoms. An ether group can for examplebe a polyether moiety such as polyoxyethylene. A carboxyl group can forexample be a carboxylic acid, salt, ester, amide or anhydride group. Thefunctional organic group can alternatively be a group havingcarbon-carbon unsaturation which reacts less readily than allyl in ahydrosilylation reaction in the presence of a noble metal catalyst, forexample a methacrylate or acrylate group. Examples of allyl compounds(B) containing a functional organic group include allyloxypropanediol(that is, allyl 2,3-dihydroxypropyl ether), allyl glycidyl ether, allylalcohol, allylamine, N-(2-ethylamino)allylamine, allyl chloride, allylmethacrylate, allyl mercaptan, 4-allyloxy-2-hydroxybenzophenone,2-allyloxy-ethanol, allyl isocyanate, 4-pentenoic acid, 10-undecenoicacid or an ester thereof such as ethyl-10-undecenoate, or anallyl-terminated polyether such as polyethoxylated allyl alcohol.

[0018] The allyl compound can alternatively be an unsubstituted 1-alkenehaving at least 4, for example 4 to 50, particularly 6 to 20, carbonatoms, used to modify the properties of a siloxane by introducing longchain alkyl groups. Examples of such 1-alkenes are 1-hexene, 1-octeneand 1-hexadecene.

[0019] For those allyl-functional starting materials that containalcohol groups COH, we have found that a second undesirableside-reaction (the reaction of SiH and COH to form SiOC and H2) issignificantly reduced by running this process continuously at hightemperature. This is important for example when producing thecommercially important silicone polyether copolymers (“siloxylatedpolyethers”).

[0020] Examples of siloxanes (A) can be represented by compounds of theformula R₃SiO(R′₂SiO)_(a)(R″HSiO)_(b)SiR₃, (I), formulaHR₂SiO(R′₂SiO)_(c)SiR₂H (II) or formulaHR₂SiO(R′₂SiO)_(a)(R″HSiO)_(b)SiR₂H (III). In these formulae, R, R′, andR″, are alkyl groups with 1-30, preferably 1-6 carbon atoms; a is 0-250;b is 1-250; and c is 0-250. Siloxanes of either type (I), (II) or (III),or two or all of these types, can be used in the reaction. Siloxanescontaining at least 2 Si—H groups per molecule may be preferred. Thesiloxane may for example have a degree of polymerisation of 10 to 80siloxane units. The siloxane (A) can also comprise an alkylhydrogencyclosiloxane or an alkylhydrogen-dialkyl cyclosiloxane copolymer,represented in general by the formula (R′₂SiO)_(a)′(R″HSiO)_(b)′, whereR′ and R″ are as defined above and where a′ is 0-7 and b′ is 3-10. Somerepresentative compounds of these types are (OSiMeH)₄,(OSiMeH)₃(OSiMeC₆H₁₃), (OSiMeH)₂(OSiMeC₆H₁₃)₂ and (OSiMeH)(OSiMeC₆H₁₃)₃,where Me represents —CH₃.

[0021] Examples of silanes (A) can be represented by the formula Z3SiH,where each Z independently represents hydrogen, halogen, an alkyl orhaloalkyl group having 1-30, preferably 1-6 carbon atoms, a phenyl groupor an alkoxy group having 1-4 carbon atoms. Preferably the groups Z areselected from methyl, chloro and alkoxy groups. Some representativesilanes (A) are trimethylsilane, triethoxysilane, methyidimethoxysilaneand trichlorosilane.

[0022] The silane or siloxane (A) and the allyl compound (B) can bemiscible or immiscible. In the case of immiscible reagents, masstransfer limitations can significantly reduce the overall process rate.In order to minimise these mass transfer limitations it is preferred tomaximise the surface area between the reactant phases, for example bycreating a dispersion of one phase in the other of a small particle sizeand high interfacial area. This can be achieved for example by mixingthe reagents (A) and (B) in any type of dynamic or static mixing devicebefore the reactor stage or by mixing elements, usually static mixingelements, incorporated in the reactor itself. Use of such static mixingelements together with a mixer before the reactor can be used ifdesired.

[0023] The reagents should be present in fluid form in the reactor.Preferably the silane or siloxane (A) and the allyl compound (B) areboth fluid, most preferably liquid, at the temperature of the reactionzone. Alternatively either of the reagents can be dissolved in a solventwhich is liquid at the temperature of the reaction zone. The reagentsare preferably pre-heated, either separately or together after mixing,to approximately the desired temperature of reaction before entering thereactor.

[0024] The reagents can be used in a ratio of SiH groups to allyl groupswithin the range 1:3 to 3:1, preferably in approximately stoichiometricequivalent amounts to minimise the need for separation of the silane orsiloxane product containing at least one functional organic group fromany unreacted reagents.

[0025] It is preferred that the catalyst is also in liquid form and thatthe catalyst is homogeneously dispersed in the liquid reaction mixture.The noble metal of the catalyst is preferably platinum, although rhodiumis an alternative. One preferred platinum catalyst is a solution ofhexachloroplatinic acid in a solvent such as xylene. Another is aplatinum divinyl tetramethyl disiloxane complex typically containingabout one weight percent of platinum in a solvent such as xylene.Another preferred platinum catalyst is a reaction product ofchloroplatinic acid and an organosilicon compound containing terminalaliphatic unsaturation. The noble metal catalyst is preferably used inamounts from 0.00001-0.5 parts per 100 weight parts of the ≡SiHcontaining silane or siloxane (A), most preferably 0.00001-0.002 parts.

[0026] The catalyst can for example be injected into the reaction zonedownstream of the point where (A) and (B) are mixed. Alternatively thecatalyst can be mixed with the allyl compound (B) before the allylcompound (B) is mixed with the silane or siloxane (A).

[0027] If the reaction system is heterogeneous, it may be preferred touse a heat exchanger reactor of the type described in WO-A-00/34728.

[0028] The silane or siloxane products containing at least onefunctional organic group have a wide variety of uses. Siloxanescontaining alcohol or ether-alcohol groups can be used as surfactants orfoam control agents. Siloxanes containing polyether groups can be usedas surfactants or foam stabilisers. Siloxanes containing hydrophilicgroups such as carboxyl, amino or epoxide groups can be used in textiletreatment. Silanes containing reactive groups such as epoxide,isocyanate, methacrylate, halide, thiol or amino groups can be used inchemical synthesis or as coupling agents for treating fillers forplastics materials.

[0029] The invention is illustrated by the following Example.

EXAMPLE 1

[0030] A silicon-hydride functional siloxane having a degree ofpolymerisation (DP) of 20 siloxane units with a 40 mole %silicon-hydride content (Si—H on 40% of Si atoms), andallyloxypropanediol, were fed in stoichiometric equivalent amounts to aninline dynamic mixer of the rotor stator type at a total feed rate of200 g/min. This reactant mix was heated to 130° C. and fed to a heatexchanger reactor of the type shown in FIGS. 1 to 6 of WO-A-99/66280.

[0031] The reactor comprised channels of diameter 1 mm and had a totalinternal volume of 29 mL. A catalyst solution of 1% hexachloroplatinicacid was directly injected into the reactor at 1 mL/min. The temperaturewithin the reactor was maintained at 130° C. The residence time of thereagents in the reactor after injection of the catalyst was 6 seconds. Aclear water-white fluid product of viscosity 20 Pa.s (20,000 cP) wasobtained at 12 kg/hour. This product was a siloxane substituted by3-(2,3-dihydroxypropoxy)propyl groups, useful as a surfactant or foamcontrol agent.

[0032] No isomerised by-product (3-(2,3-dihydroxypropoxy)propene-2)could be detected in the product, indicating a level of isomerisation ofless than 0.1 mole %.

[0033] In a comparative experiment, allyloxypropanediol and 1% of the !%hexachloroplatinic acid catalyst solution were charged to a 200 L batchreactor with 100 L isopropanol solvent. The silicon-hydride functionalsiloxane was fed to the reactor over a period of 4 hours, the total feedbeing stoichiometrically equivalent to the allyl compound. Temperaturewas maintained at 80° C. with cooling. The isopropanol solvent wasnecessary to allow sufficient cooling of the exothermic hydrosilylationreaction. After four hours isopropanol was removed by stripping. Thefinal product was a straw-coloured viscous liquid siloxane substitutedby 3-(2,3-dihydroxypropoxy)propyl groups, but this contained 30 mole %of isomerised unsaturated monomer by-products.

EXAMPLE 2

[0034] Heptamethyltrisiloxane and 1-octene(an allyl group containingcompound) were fed in stoichimetric equivalent amounts to the sameexperimental setup described in example 1—ie an inline dynamic mixer anda heat exchanger reactor. This system is a miscible, homogeneous system.A catalyst solution of 0.6% Pt(as metal) in a divinyl tetramethyldisiloxane complex was directly injected to the reactor at 17 ml/minute.The temperature within the reactor was maintained at 150 deg C., andresidence time was approximately 11 seconds at the 160 g/min overallflowrate employed. Virtually complete single pass conversion to1,1,1,2,3,3,3-heptamethyl-2-octyltrisiloxane fluid product occurred,with approximately 2.5% isomerization of the octene occurring.

What is claimed is:
 1. A process for the preparation of a silane or asiloxane containing at least one organic group, wherein a silane orsiloxane (A) containing at least one Si—H group and an allyl compound(B) are fed continuously through a reaction zone in the presence of anoble metal catalyst, whereby the silane or siloxane (A) and the allylcompound (B) react in an exothermic hydrosilylation reaction, thereaction zone being maintained at a temperature in the range 115-200° C.and being provided with a heat exchanger means to dissipate the heatfrom the exothermic hydrosilylation reaction, and the residence time of(A) and (B) in the reaction zone being less than 20 minutes.
 2. Aprocess according to claim 1 wherein the reaction zone comprises narrowchannels in a block of material of high heat conductivity.
 3. A processaccording to claim 2 wherein the channels have a thickness of less than2 mm.
 4. A process according to claim 1 wherein (A) and (B) are mixed toform a dispersion before they enter the reaction zone.
 5. A processaccording to claim 1 wherein the reaction zone contains static mixingelements to promote mixing of (A) and (B).
 6. A process according toclaim 1 wherein the reaction zone is maintained at a temperature in therange 130-160° C.
 7. A process according to claim 6 wherein theresidence time of (A) and (B) in the reaction zone is less than 30seconds.
 8. A process according to claim 7 wherein the residence time of(A) and (B) in the reaction zone is from 1 to 15 seconds.
 9. A processaccording to claim 1 wherein the catalyst is homogeneously dispersed inthe liquid reaction mixture.
 10. A process according to claim 1 whereinthe catalyst is injected into the reaction zone downstream of the pointwhere (A) and (B) are mixed.
 11. A process according to claim 1 whereinthe catalyst is mixed with the allyl compound (B) before the allylcompound (B) is mixed with the silane or siloxane (A).
 12. A processaccording to claim 1 for the preparation of a silane or siloxanecontaining at least one functional organic group selected from the groupconsisting of hydroxyl, epoxide, isocyanate, amine, methacrylate,halide, ether and carboxyl, wherein the allyl compound (B) contains agroup selected from the group consisting of hydroxyl, epoxide,isocyanate, amine, methacrylate, halide, ether or carboxyl group.
 13. Aprocess according to claim 1 wherein (A) is a siloxane containing atleast 2 Si—H groups per molecule.
 14. A process according to claim 12wherein the allyl compound (B) is allyloxypropanediol.
 15. A processaccording to claim 12 wherein the level of isomerised allyl compoundby-product produced is less than 5 mole % based on the amount offunctional organic groups derived from allyl compound (B) incorporatedin the siloxane.